The field of this invention is the modulation of NO activity, which finds application in maintaining and improving vascular function and thereby preventing or improving vascular degenerative diseases.
Atherosclerosis and vascular thrombosis are a major cause of morbidity and mortality, leading to coronary artery disease, myocardial infarction, and stroke. Atherosclerosis begins with an alteration in the endothelium, which lines the blood vessels. The endothelial alteration results in adherence of monocytes, which penetrate the endothelial lining and take up residence in the subintimal space between the endothelium and the vascular smooth muscle of the blood vessels. The monocytes absorb increasing amounts of cholesterol (largely in the form of oxidized or modified low-density lipoprotein) to form foam cells. Oxidized low-density lipoprotein (LDL) cholesterol alters the endothelium, and the underlying foam cells distort and eventually may even rupture through the endothelium.
Platelets adhere to the area of endothelial disruption and release a number of growth factors, including platelet derived growth factor (PDGF). PDGF, which is also released by foam cells and altered endothelial cells, stimulates migration and proliferation of vascular smooth muscle cells into the lesion. These smooth muscle cells release extracellular matrix (collagen and elastin) and the lesion continues to expand. Macrophages in the lesion elaborate proteases, and the resulting cell damage creates a necrotic core filled with cellular debris and lipid. The lesion is then referred to as a xe2x80x9ccomplex lesion.xe2x80x9d Rupture of this lesion can lead to thrombosis and occlusion of the blood vessel. In the case of a coronary artery, rupture of a complex lesion may precipitate a myocardial infarction, whereas in the case of a carotid artery, stroke may ensue.
One of the treatments that cardiologists and other interventionalists employ to reopen a blood vessel which is narrowed by plaque is balloon angioplasty (approximately 300,000 coronary and 100,000 peripheral angioplasties are performed annually). Although balloon angioplasty is successful in a high percentage of the cases in opening the vessel, it unfortunately denudes the endothelium and injures the vessel in the process. This damage causes the migration and proliferation of vascular smooth muscle cells of the blood vessel into the area of injury to form a lesion, known as myointimal hyperplasia or restenosis. This new lesion leads to a recurrence of symptoms within three to six months after the angioplasty in a significant proportion of patients (30-40%).
In atherosclerosis, thrombosis and restenosis there is also a loss of normal vascular function, such that vessels tend to constrict, rather than dilate. The excessive vasoconstriction of the vessel causes further narrowing of the vessel lumen, limiting blood flow. This can cause symptoms such as angina (if a heart artery is involved), or transient cerebral ischemia (i.e. a xe2x80x9csmall strokexe2x80x9d, if a brain vessel is involved). This abnormal vascular function (excessive vasoconstriction or inadequate vasodilation) occurs in other disease states as well. Hypertension (high blood pressure) is caused by excessive vasoconstriction, as well as thickening, of the vessel wall, particularly in the smaller vessels of the circulation. This process may affect the lung vessels as well causing pulmonary (lung) hypertension. Other disorders known to be associated with excessive vasoconstriction, or inadequate vasodilation include transplant atherosclerosis, congestive heart failure, toxemia of pregnancy, Raynaud""s phenomenon, Prinzmetal""s angina (coronary vasospasm), cerebral vasospasm, hemolytic-uremia and impotence.
Because of their great prevalence and serious consequences, it is critically important to find therapies which can diminish the incidence of atherosclerosis, vascular thrombosis, restenosis, and these other disorders characterized by abnormality of vascular function and structure. Ideally, such therapies would inhibit the pathological vascular processes associated with these disorders, thereby providing prophylaxis, retarding the progression of the degenerative process, and restoring normal vasodilation.
As briefly summarized above, these pathological processes are extremely complex, involving a variety of different cells which undergo changes in their character, composition, and activity, as well as in the nature of the factors which they secrete and the receptors that are up- or down-regulated. A substance released by the endothelium, xe2x80x9cendothelium derived relaxing factorxe2x80x9d (EDRF), may play an important role in inhibiting these pathologic processes. EDRF is now known to be nitric oxide (NO) or a labile nitroso compound which liberates NO. (For purposes of the subject invention, unless otherwise indicated, nitric oxide (NO) shall intend nitric oxide or the labile nitroso compound which liberates NO.) This substance relaxes vascular smooth muscle, inhibits platelet aggregation, inhibits mitogenesis and proliferation of cultured vascular smooth muscle, and leukocyte adherence. Because NO is the most potent endogenous vasodilator, and because it is largely responsible for exercise-induced vasodilation in the conduit arteries, enhancement of NO synthesis could also improve exercise capacity in normal individuals and those with vascular disease. NO may have other effects, either direct or indirect, on the various cells associated with vascular walls and degenerative diseases of the vessel.
Girerd et al. (1990) Circulation Research 67:1301-1308 report that intravenous administration of L-arginine potentiates endothelium-dependent relaxation in the hind limb of cholesterol-fed rabbits. The authors conclude that synthesis of EDRF can be increased by L-arginine in hypercholesterolemia. Rossitch et al. (1991) J. Clin. Invst. 87:1295-1299 report that in vitro administration of L-arginine to basilar arteries of hypercholesterolemic rabbits reverses the impairment of endothelium-dependent vasodilation and reduces vasoconstriction. They conclude that the abnormal vascular responses in hypercholesterolemic animals is due to a reversible reduction in intracellular arginine availability for metabolism to nitric oxide.
Creager et al. (1992) J. Clin. Invest. 90:1248-1253, report that intravenous administration of L-arginine improves endothelium-derived NO-dependent vasodilation in hypercholesterolemic patients.
Cooke et al., xe2x80x9cEndothelial Dysfunction in Hypercholesterolemia is Corrected by L-arginine,xe2x80x9d Endothelial Mechanisms of Vasomotor Control, eds. Drexler, Zeiher, Bassenge, and Just; Steinkopff Verlag Darmstadt, 1991, pp. 173-181, review the results of the earlier references and suggest, xe2x80x9cIf the result of these investigations may be extrapolated, exogenous administration of L-arginine (i.e., in the form of dietary supplements) might represent a therapeutic adjunct in the treatment and/or prevention of atherosclerosisxe2x80x9d.
Cooke (1990) Current Opinion in Cardiology 5:637-644 discusses the role of the endothelium in the atherosclerosis and restenosis, and the effect that these disorders have on endothelial function.
Cooke (1992) J. Clin. Invest. 90:1168-1172, describe the effect of chronic administration of oral L-arginine in hypercholesterolemic animals on atherosclerosis. This is the first demonstration that oral L-arginine supplements can improve the release of NO from the vessel wall. The increase in NO release from the vessel wall was associated with a striking reduction in atherosclerosis in hypercholesterolemic animals. This is the first evidence to support the hypothesis that increasing NO production by the vessel wall inhibits the development of atherosclerosis.
Cooke and Tsao (1992) Current Opinion in Cardiology 7:799-804 describe the mechanism of the progression of atherosclerosis and suggest that inhibition of nitric oxide may disturb vascular homeostasis and contribute to atherogenesis.
Cooke and Santosa (1993) In: Steroid Hormones and Dysfunctional Bleeding, AAAS Press, review the activities of EDRF in a variety of roles and suggest that reversibility of endothelial dysfunction may be affected by the stage of atherosclerosis. They conclude that EDRF is a potent vasodilator, plays a key role in modulating conduit and resistance vessel tone, has important effects on cell growth and interactions of circulatory blood cells with a vessel wall, and that disturbances of EDRF activity may initiate or contribute to septic shock, hypertension, vasospasm, toxemia and atherosclerosis.
Fitzpatrick et al., American Journal of Physiology 265 (Heart Circ. Physiol. 34):H774-H778, 1993 report that wine and other grape products may have endothelium-dependent vasorelaxing activity in vitro.
Wang et al. (1994) J. Am. Cell. Cardiol. 23:452-458, report that oral administration of arginine prevents atherosclerosis in the coronary arteries of hypercholesterolemic rabbits.
Drexler et al. (1994) Circulation 89:1615-1623 describe the effect of intravenous arginine upon coronary vascular tone. This was the first evidence that intravenous arginine could restore normal NO-dependent vasodilation in the coronary arteries of patients with cardiac transplants, Tsao et al. (1994) Circulation 89:2176-2182 demonstrates that oral administration of arginine to hypercholesterolemic rabbits enhances the release of nitric oxide by the vessel wall, and inhibits monocytes from sticking to the vessel.
Tsao et al. (1994) J. Arterioscl. Thromb. 14:1529-1533 reveals that oral arginine administration to hypercholesterolemic rabbits inhibits platelet aggregation (blood clotting). Platelet aggregation plays an important role in causing vascular thrombosis in vascular degenerative disorders.
Von de Leyen et al. (1995) PNAS USA, show that the gene encoding nitric oxide synthase (the enzyme that produces NO) can be inserted into the carotid artery of the rat. This causes the rat carotid artery to make more NO, and thereby enhances vasodilation and inhibits thickening of the vessel wall after balloon angioplasty.
Noruse et al. (1994) Arterioscler. Thromb. 14:746-752, report that oral administration of an antagonist of NO production accelerates atherogenesis in hypercholesterolemic rabbits.
Cayette et al. (1994) Arterioscler. Thromb. 14:753-759, also report that oral administration of an antagonist of NO production accelerates plaque development in hypercholesterolemic rabbits.
Other references which refer to activities attributed to NO or its precursor include: Pohl and Busse (1989) Circ. Res. 65:1798-1803; Radomski et al. (1987) Br. J. Pharmacol. 92:181-187; Stamler et al. (1989) Circ. Res. 65:789-795; anti-platelet activity); Garg and Hassid (1989) J. Clin. Invest. 83:1774-1777; Weidinger et al. (1990) Circulation 81:1667-1679; NO activity in relation to vascular smooth muscle growth); Ross (1986) N. Engl. J. Med. 314:488-500; Bath et al. (1991) Arterioscler. Thromb. 11:254-260; Kubes et al. (1991) Proc. Natl. Acad. Sci. USA 89:6348-6352; Lefer et al. (1990) In: Endothelium-Derived Contracting Factors. Basel, S. Karger, pp.190-197; NO activity in relation to leukocyte adhesion and migration); Heistad et al. (1984) Circ. Res. 43:711-718; Rossitch et al. (1991) J. Clin. Invest. 87:1295-1299; Yamamoto et al. (1988) ibid 81:1752-1758; Andrews et al. (1987) Nature 327:237-239; Tomita et al. (1990) Circ. Res. 66:18-27; Kugiyama et al. (1990) Nature 344:160-162; Mitchell et al. (1992) J. Vasc. Res. 29:169 (abst.); Minor et al. (1990) J. Clin. Invest. 86:2109-2116; NO activity in relation to hypercholesterolemia); Tanner et al. (1991) Circulation 83:2012-2020; Kuo et al. (1992) Circ. Res. 70:f465-476; Drexler et al. (1991) Lancet 338:1546-1550; Schuschke et al. (1994) Int. J. of Microcircu: Clin. and Exper. 14(4):204-211; Yao et al. (1992) Circulation 86:1302-1309; Higashi et al. (1995) Hypertension 25(4 Pt 2):898-902; Kharitonov et al. (1995) Clin. Sci. 88(2):135-139; Smulders et al. (1994) Clin. Sci. 87(1):37-43; Bode-boger et al. (1994) Clin. Sci. 87(3):303-310; Bode-Boger et al. (1994) Clin. Sci.; Randall et al. (1994) Clin. Sci. 87(1):53-59; Dubois-Rande et al. (1992) J. Card. Pharm. 20 Suppl. 12:S211-3; Otsuji et al. (1995) Am. Heart J. 129(6): 1094-1100; Nakanishi et al. (1992) Am. J. of Physio. 263(6 Pt 2):H1650-8; Kuo et al. (1992) Circ. Research 70(3): 465-476; Tanner et al. (1991) Circulation 83(6):2012-2020; Meng et al. (1995) J. Am. Col. Card. 25(l):269-275; Lefer and Ma (1993) Arterioscl. and Thromb. 13(6):771-776; McNamara et al. (1993) Biochem. and Biophys. Res. Comm. 193(1):291-296; Tarry and Makhoul (1994) Arter. and Thromb. 14(6):983-943; Davies et al. (1994) Surgery 116(3):557-568; and Raij (1994) Kidney Institute 45:775-781.
Methods are provided for improving vascular function and structure, particularly modulating vascular relaxation, cellular adhesion, infiltration and proliferation by modulating the level of nitric oxide or active precursor at a physiological site. The methods find use in preventing the degradation of vascular function, particularly as involved with the occurrence of atherosclerosis, restenosis, thrombosis, hypertension, impotence, and other disorders characterized by reduced or inadequate vasodilation. The enhancement of endogenous nitric oxide or secondary messenger availability at a physiological site improves vascular relaxation and thereby relieves symptoms due to inadequate blood flow (such as angina) and can counteract inappropriate elevation of blood pressure. The enhancement of endogenous nitric oxide also inhibits initiation and the progression of atherosclerosis, restenosis, vascular hypertrophy or hyperplasia and thrombosis. This is due to the fact that nitric oxide is not only a potent modulator, but can also inhibit platelets and white blood cells from adhering to the vessel wall. As a prophylaxis or treatment for vascular function deterioration, particularly in atherosclerotic susceptible hosts, the agent is chronically administered at an effective dosage. For restenosis, the agent may be administered for a limited period since this pathological process generally abates 3-6 months after the vascular injury (i.e. angioplasty or atherectomy). Oral administration of L-arginine, precursors to L-arginine, e.g. oligopeptides or polypeptides comprising L-arginine, or proteins comprising high levels of L-arginine, by itself or in combination with L-lysine, particularly further supplemented with GRAS substances which enhance the effectiveness of the active agents, as a dietary supplement will increase NO elaboration and thereby diminish the effects of atherogenesis. Other techniques to enhance NO or secondary messenger availability may be utilized such as increasing the availability of NO synthase, for example, as a result of enhanced expression of NO synthase in the vessel wall, particularly at the lesion site, release of NO from the vessel wall or reduction of degradation of NO or the secondary messenger, cyclic guanosine monophosphate (xe2x80x9ccGMPxe2x80x9d).